This invention relates broadly to an automatic welding apparatus for performing welding operations on comparatively large and long workpieces and more particularly to an arrangement wherein a movable base is utilized to support either a composite, welding torch carrying frame or workpiece holder such that the frame and holder are relatively movable with respect to one another along a longitudinal axis.
In order to accomplish the automatic welding of a workpiece in three dimensions, the conventional apparatus provides the welding torch or tool with the capability of being movably located within a three dimensional space which defines the operational limits of the apparatus. Customarily the workpiece to be welded is mounted within the reach of the tool by a stationary workpiece holder which is affixed to a floor plate. Problems arise with this arrangement when a workpiece needs to be welded which has dimensions that exceed the reach of the tool. In order to bring all points of the workpiece within reach of the tool, a plurality of set-ups would be required. Each set-up involves an operator removing the workpiece from its holder so that previously unobtainable points on the workpiece are brought into the reach of the tool. Accordingly, the set-up operation requires that all welding be suspended while the workpiece is being remounted. This reduces work efficiency; and decreases the accuracy of the welding operation since a plurality of location points are necessary to orient the workpiece with respect to the apparatus' spacial positioning reference frame. If a heavy workpiece is being welded, the risk of an industrial accident is increased when the use of a crane or other transport device is necessitated.
In order to eliminate the need for a number of set-ups, it is known in the prior art to provide an automatic welding apparatus with a workpiece holder structure which provides the necessary degree of freedom of movement to present a workpiece to a fixed welding tool. This approach involves the use of a workpiece holder structure that is extremely complex, and adds to the overall cost of manufacture as well as demanding increased maintenance considerations.
Another prior art approach is disclosed in Oda et al. U.S. Pat. No. (4,014,495) which relates to an automatic welding apparatus that combines a movable workpiece holder with a welding tool capable of being positioned at any point within a three dimensional space. The tool is attached to a composite frame adapted to provide movement in three mutually orthogonal directions such as in the longitudinal, lateral, and vertical direction, and may be rotated around a vertical axis. The workpiece holder is adapted to be rotated around a horizontal axis. The position of the workpiece holder is controlled by a servo system under the command of a programmable computer device. Although larger workpieces can be handled by such an arrangement, the primary object of the Oda invention is to provide an automatic welding apparatus wherein the necessary degree of freedom of movement is divided between a workpiece holder and a welding tool. This prior art approach also has similar faults aforesaid when a workpiece needs to be welded which has dimensions that exceed the reach of the tool.